The present invention generally pertains to intravascular devices. In particular, the present invention pertains to intravascular thrombosis filters.
Pulmonary embolism is a recognized medical emergency, and is often caused by venous thrombosis. Physiological conditions such as venous intima damage, blood flow retention, and coagulation abnormalities are often the cause of venous thrombosis. Recognized treatments for venous thrombosis include anti-coagulant medication therapy, thrombolytic therapy, thrombectomy, and inferior vena cava thrombosis filtering or blocking procedures.
When an inferior vena cava thrombosis filtering or blocking procedure is selected, it can be performed using either a laparotomy procedure, or by percutaneously inserting a thrombosis filter. A laparotomy procedure is a surgical procedure performed under general anesthesia. Because it is necessary to discontinue anti-coagulant therapy prior to surgery, this procedure, itself, is susceptible to thrombosis formation.
The second option is to intravenously insert a thrombosis filter into the vascular system. In particular, the thrombosis filter is mounted into the inferior vena cava in order to prevent large emboli from passing to the lungs. Since this procedure requires only a local anesthetic, percutaneous filter insertion is recognized as an effecateous procedure. Thrombosis filters, however, become encapsulated to the vein wall through neointimal hyperplasia. Neointimal hyperplasia is the subsequent increase in endothelial cell production caused by the irritation of the lining membrane of the blood vessel. Neointima grows from the inner wall of the blood vessel, around the thrombosis filter and its anchors. This process can occur within two or three weeks after implantation, rendering many thrombosis filters unremovable by a single percutaneous process without significant vessel trauma.
The present invention comprises a thrombosis filter having various surface treatments. In each preferred embodiment of the thrombosis filter of the present invention, the filter includes a body element, a plurality of struts, and a surface treatment.
The body element serves as the support structure to which the plurality of struts are attached. Generally, the struts are attached to the body element and extend longitudinally and radially therefrom forming a generally conical structure. The struts, themselves, are shaped and spaced apart in a manner which allows them to prevent emboli from passing into the lungs via the circulatory system when in use in a vessel lumen. Each individual strut has both a joining end and a free end. The joining end of the strut is secured to the body element. The free end of the strut, however, extends away from the body element and bears against the inner wall of the blood vessel. Vessel-engaging tips of various designs may be placed on the free end of a strut in order to facilitate the strut""s engagement with the blood vessel wall. The combination of the body element with its plurality of struts radiating therefrom brace the thrombosis filter against the inner wall of the blood vessel within the blood vessel lumen.
A surface treatment is applied to at least a portion of the thrombosis filter in order to regulate neointimal growth around the thrombosis filter and its anchor elements. Inhibiting the neointimal growth allows for the removal of the thrombosis filter with reduced retrieval forces and limited damage to the vessel wall. The surface treatment in preferred embodiments constitutes, in part, an anti-proliferative or an anti-angiogenesis drug.
In one embodiment, the drug is an anti-angiogenesis agent. Anti-angiogenesis agents are substances which have the ability to impede the local proliferation of blood vessels, thereby blocking the necessary xe2x80x9cfood supplyxe2x80x9d of the growing endothelial cell mass. This anti-angiogenesis drug may be coated directly upon portions of the thrombosis filter, itself, through a dipping or spraying process, or the drug may be incorporated into a polymeric material as a carrier which regulates the rate of drug release to the vessel wall.
In a further embodiment, the thrombosis filter contains a first and a second surface treatment layer. The first surface treatment layer, coated upon at least a portion of the thrombosis filter, possesses endothelial cell growth enhancing properties. The second surface treatment layer, coated upon at least a portion of the first surface layer, includes an anti-proliferative or an anti-angiogenesis drug. In this arrangement, the second surface treatment layer is dissolvable or generally biodegradable. Thus, when the filter is first placed in the vessel lumen, the anti-proliferative or anti-angiogenesis drug inhibits neointimal growth as discussed above. However, if the thrombosis filter remains engaged with the vessel wall for an extended period, the second layer will dissolve exposing the first layer. The first layer then promotes endothelial cell growth causing the eventual permanent encapsulation of the anchor elements of the filter within the blood vessel wall.
The surface treatment may be applied directly to a portion of the filter or the surface treatment may be applied to a substrate which, in turn, is applied to a portion of the filter. Preferably, the substrate is disposed about the free ends of the struts and may take the form of a pad, a tubular structure, or a band.
The present invention is thus an improved thrombosis filter. Additional features of the invention and the advantages derived therefrom, and the various scopes and aspects of the invention will become apparent from the drawings, the description of the preferred embodiments of the invention, and the claims.